security
networking
DNS filtering
Also known as: DNS filter, protective DNS, PDNS
Blocking risky or policy-violating domains at the DNS resolver layer, before a TCP connection is ever attempted.
DNS filtering intercepts every DNS query a device makes and returns either the real answer or a block (NXDOMAIN, a sinkhole IP, or a redirect to a “blocked by policy” page).
Why it’s the cheapest, highest-leverage security control an MSP can deploy:
- Pre-connection enforcement, the user’s browser never even tries to reach the malicious site
- No client agent required for many deployments (set the resolver IPs at the network edge)
- Visibility everywhere, every device, IoT included, hits DNS
- Categorisation by threat (malware, phishing, C2) and content (gambling, social, adult)
Common products: DNSFilter, Cisco Umbrella, Cloudflare Gateway, WebTitan. Some operate via on-network resolver IPs; others ship a lightweight roaming client for off-LAN coverage.